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Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Hi, I got a 15A 0-140V variac and it seems to be shorted somewhere when power is applied. I measured the inductance of the 120V side and I got 1.8H. When I connected it to the line it hummed and then tripped the breaker after a couple seconds. I took it appart and found nothing wrong with it. On the side plate it said that it was rated for 400CY. Does this mean 400Hz? Is it okay to run it on 60Hz? What do they use 400Hz for anyways? I have a smaller variac that is also rated for 400Hz but also 60Hz. If I can't run it on 60Hz what could I use it for?
Registered Member #528
Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166
What exactly was rated? Perhaps you should give a photo of plate. Was variac powered without ballast or soft-start circuit? Without that, my 2.2kVA variac would trip breaker instantly, but if it's couple seconds for you, then I'm not sure if it's a inrush current issue.. (with big toroid, a few of kVA's, it's almost certain that when you plug it to mains, a big current damps into and trips breaker/fuse).
Registered Member #187
Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140
Aren't iron laminate transformers claimed to be okay to use up around 400Hz, or is it 4000Hz? I can't remember what the upper cutoff frequency is for a common transformer, but at first I thought that's what you were seeing, the maximum applicable frequency.
After seeing the way it's stated on the plate, I'm with Gigavolt, the core is saturating (and if it's rated for 400Hz, it's saturating rather quickly) and causing a rather large current draw from your mains.
The only way I can think that you could still use that variac on 120V @60Hz is to ballast it with a large inductor, such as another transformers primary.
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
could the variac run on a 400hz squarewave?. I ask this because i have ran iron cored ignition coils with a squarewave up to frequencies as high as 20khz without any saturation problem.
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Variac questions
